"Do not make friends with a hot-tempered man, do not associate with one easily angered, or you may learn his ways and get yourself ensnared." Proverbs 22:24-25

"A hot-tempered man must pay the penalty; if you rescue him, you will have to do it again." Proverbs 19:19

"A man of knowledge uses words with restraint, and a man of understanding is even-tempered." Proverbs 17:27

More about being slow to anger: "A hot-tempered man stirs up dissension, but a patient man calms a quarrel." Proverbs 15:18

"A fool shows his annoyance at once, but a prudent man overlooks an insult." Proverbs 12:16